package im.actor.crypto.primitives.curve25519;

public class fe_mul {

//CONVERT #include "fe.h"
//CONVERT #include "long.h"

/*
h = f * g
Can overlap h with f or g.

Preconditions:
   |f| bounded by 1.65*2^26,1.65*2^25,1.65*2^26,1.65*2^25,etc.
   |g| bounded by 1.65*2^26,1.65*2^25,1.65*2^26,1.65*2^25,etc.

Postconditions:
   |h| bounded by 1.01*2^25,1.01*2^24,1.01*2^25,1.01*2^24,etc.
*/

/*
Notes on implementation strategy:

Using schoolbook multiplication.
Karatsuba would save a little in some cost models.

Most multiplications by 2 and 19 are 32-bit precomputations;
cheaper than 64-bit postcomputations.

There is one remaining multiplication by 19 in the carry chain;
one *19 precomputation can be merged into this,
but the resulting data flow is considerably less clean.

There are 12 carries below.
10 of them are 2-way parallelizable and vectorizable.
Can get away with 11 carries, but then data flow is much deeper.

With tighter constraints on inputs can squeeze carries into int32.
*/

  private static long[] fe_mul1(int[] f,int[] g){
    int f0 = f[0];
    int f1 = f[1];
    int f2 = f[2];
    int f3 = f[3];
    int f4 = f[4];
    int f5 = f[5];
    int f6 = f[6];
    int f7 = f[7];
    int f8 = f[8];
    int f9 = f[9];
    int g0 = g[0];
    int g1 = g[1];
    int g2 = g[2];
    int g3 = g[3];
    int g4 = g[4];
    int g5 = g[5];
    int g6 = g[6];
    int g7 = g[7];
    int g8 = g[8];
    int g9 = g[9];
    int g1_19 = 19 * g1; /* 1.959375*2^29 */
    int g2_19 = 19 * g2; /* 1.959375*2^30; still ok */
    int g3_19 = 19 * g3;
    int g4_19 = 19 * g4;
    int g5_19 = 19 * g5;
    int g6_19 = 19 * g6;
    int g7_19 = 19 * g7;
    int g8_19 = 19 * g8;
    int g9_19 = 19 * g9;
    int f1_2 = 2 * f1;
    int f3_2 = 2 * f3;
    int f5_2 = 2 * f5;
    int f7_2 = 2 * f7;
    int f9_2 = 2 * f9;
    long f0g0    = f0   * (long) g0;
    long f0g1    = f0   * (long) g1;
    long f0g2    = f0   * (long) g2;
    long f0g3    = f0   * (long) g3;
    long f0g4    = f0   * (long) g4;
    long f0g5    = f0   * (long) g5;
    long f0g6    = f0   * (long) g6;
    long f0g7    = f0   * (long) g7;
    long f0g8    = f0   * (long) g8;
    long f0g9    = f0   * (long) g9;
    long f1g0    = f1   * (long) g0;
    long f1g1_2  = f1_2 * (long) g1;
    long f1g2    = f1   * (long) g2;
    long f1g3_2  = f1_2 * (long) g3;
    long f1g4    = f1   * (long) g4;
    long f1g5_2  = f1_2 * (long) g5;
    long f1g6    = f1   * (long) g6;
    long f1g7_2  = f1_2 * (long) g7;
    long f1g8    = f1   * (long) g8;
    long f1g9_38 = f1_2 * (long) g9_19;
    long f2g0    = f2   * (long) g0;
    long f2g1    = f2   * (long) g1;
    long f2g2    = f2   * (long) g2;
    long f2g3    = f2   * (long) g3;
    long f2g4    = f2   * (long) g4;
    long f2g5    = f2   * (long) g5;
    long f2g6    = f2   * (long) g6;
    long f2g7    = f2   * (long) g7;
    long f2g8_19 = f2   * (long) g8_19;
    long f2g9_19 = f2   * (long) g9_19;
    long f3g0    = f3   * (long) g0;
    long f3g1_2  = f3_2 * (long) g1;
    long f3g2    = f3   * (long) g2;
    long f3g3_2  = f3_2 * (long) g3;
    long f3g4    = f3   * (long) g4;
    long f3g5_2  = f3_2 * (long) g5;
    long f3g6    = f3   * (long) g6;
    long f3g7_38 = f3_2 * (long) g7_19;
    long f3g8_19 = f3   * (long) g8_19;
    long f3g9_38 = f3_2 * (long) g9_19;
    long f4g0    = f4   * (long) g0;
    long f4g1    = f4   * (long) g1;
    long f4g2    = f4   * (long) g2;
    long f4g3    = f4   * (long) g3;
    long f4g4    = f4   * (long) g4;
    long f4g5    = f4   * (long) g5;
    long f4g6_19 = f4   * (long) g6_19;
    long f4g7_19 = f4   * (long) g7_19;
    long f4g8_19 = f4   * (long) g8_19;
    long f4g9_19 = f4   * (long) g9_19;
    long f5g0    = f5   * (long) g0;
    long f5g1_2  = f5_2 * (long) g1;
    long f5g2    = f5   * (long) g2;
    long f5g3_2  = f5_2 * (long) g3;
    long f5g4    = f5   * (long) g4;
    long f5g5_38 = f5_2 * (long) g5_19;
    long f5g6_19 = f5   * (long) g6_19;
    long f5g7_38 = f5_2 * (long) g7_19;
    long f5g8_19 = f5   * (long) g8_19;
    long f5g9_38 = f5_2 * (long) g9_19;
    long f6g0    = f6   * (long) g0;
    long f6g1    = f6   * (long) g1;
    long f6g2    = f6   * (long) g2;
    long f6g3    = f6   * (long) g3;
    long f6g4_19 = f6   * (long) g4_19;
    long f6g5_19 = f6   * (long) g5_19;
    long f6g6_19 = f6   * (long) g6_19;
    long f6g7_19 = f6   * (long) g7_19;
    long f6g8_19 = f6   * (long) g8_19;
    long f6g9_19 = f6   * (long) g9_19;
    long f7g0    = f7   * (long) g0;
    long f7g1_2  = f7_2 * (long) g1;
    long f7g2    = f7   * (long) g2;
    long f7g3_38 = f7_2 * (long) g3_19;
    long f7g4_19 = f7   * (long) g4_19;
    long f7g5_38 = f7_2 * (long) g5_19;
    long f7g6_19 = f7   * (long) g6_19;
    long f7g7_38 = f7_2 * (long) g7_19;
    long f7g8_19 = f7   * (long) g8_19;
    long f7g9_38 = f7_2 * (long) g9_19;
    long f8g0    = f8   * (long) g0;
    long f8g1    = f8   * (long) g1;
    long f8g2_19 = f8   * (long) g2_19;
    long f8g3_19 = f8   * (long) g3_19;
    long f8g4_19 = f8   * (long) g4_19;
    long f8g5_19 = f8   * (long) g5_19;
    long f8g6_19 = f8   * (long) g6_19;
    long f8g7_19 = f8   * (long) g7_19;
    long f8g8_19 = f8   * (long) g8_19;
    long f8g9_19 = f8   * (long) g9_19;
    long f9g0    = f9   * (long) g0;
    long f9g1_38 = f9_2 * (long) g1_19;
    long f9g2_19 = f9   * (long) g2_19;
    long f9g3_38 = f9_2 * (long) g3_19;
    long f9g4_19 = f9   * (long) g4_19;
    long f9g5_38 = f9_2 * (long) g5_19;
    long f9g6_19 = f9   * (long) g6_19;
    long f9g7_38 = f9_2 * (long) g7_19;
    long f9g8_19 = f9   * (long) g8_19;
    long f9g9_38 = f9_2 * (long) g9_19;
    long h[] = new long[10];
    h[0] = f0g0+f1g9_38+f2g8_19+f3g7_38+f4g6_19+f5g5_38+f6g4_19+f7g3_38+f8g2_19+f9g1_38;
    h[1] = f0g1+f1g0   +f2g9_19+f3g8_19+f4g7_19+f5g6_19+f6g5_19+f7g4_19+f8g3_19+f9g2_19;
    h[2] = f0g2+f1g1_2 +f2g0   +f3g9_38+f4g8_19+f5g7_38+f6g6_19+f7g5_38+f8g4_19+f9g3_38;
    h[3] = f0g3+f1g2   +f2g1   +f3g0   +f4g9_19+f5g8_19+f6g7_19+f7g6_19+f8g5_19+f9g4_19;
    h[4] = f0g4+f1g3_2 +f2g2   +f3g1_2 +f4g0   +f5g9_38+f6g8_19+f7g7_38+f8g6_19+f9g5_38;
    h[5] = f0g5+f1g4   +f2g3   +f3g2   +f4g1   +f5g0   +f6g9_19+f7g8_19+f8g7_19+f9g6_19;
    h[6] = f0g6+f1g5_2 +f2g4   +f3g3_2 +f4g2   +f5g1_2 +f6g0   +f7g9_38+f8g8_19+f9g7_38;
    h[7] = f0g7+f1g6   +f2g5   +f3g4   +f4g3   +f5g2   +f6g1   +f7g0   +f8g9_19+f9g8_19;
    h[8] = f0g8+f1g7_2 +f2g6   +f3g5_2 +f4g4   +f5g3_2 +f6g2   +f7g1_2 +f8g0   +f9g9_38;
    h[9] = f0g9+f1g8   +f2g7   +f3g6   +f4g5   +f5g4   +f6g3   +f7g2   +f8g1   +f9g0   ;

    return h;
  }

  public static void fe_mul(int[] h,int[] f,int[] g)
  {

    long hr[] = fe_mul1(f, g);

    long carry0;
    long carry1;
    long carry2;
    long carry3;
    long carry4;
    long carry5;
    long carry6;
    long carry7;
    long carry8;
    long carry9;

  /*
  |h0| <= (1.65*1.65*2^52*(1+19+19+19+19)+1.65*1.65*2^50*(38+38+38+38+38))
    i.e. |h0| <= 1.4*2^60; narrower ranges for h2, h4, h6, h8
  |h1| <= (1.65*1.65*2^51*(1+1+19+19+19+19+19+19+19+19))
    i.e. |h1| <= 1.7*2^59; narrower ranges for h3, h5, h7, h9
  */

    carry0 = (hr[0] + (long) (1<<25)) >> 26; hr[1] += carry0; hr[0] -= carry0 << 26;
    carry4 = (hr[4] + (long) (1<<25)) >> 26; hr[5] += carry4; hr[4] -= carry4 << 26;
  /* |h0| <= 2^25 */
  /* |h4| <= 2^25 */
  /* |h1| <= 1.71*2^59 */
  /* |h5| <= 1.71*2^59 */

    carry1 = (hr[1] + (long) (1<<24)) >> 25; hr[2] += carry1; hr[1] -= carry1 << 25;
    carry5 = (hr[5] + (long) (1<<24)) >> 25; hr[6] += carry5; hr[5] -= carry5 << 25;
  /* |h1| <= 2^24; from now on fits into int32 */
  /* |h5| <= 2^24; from now on fits into int32 */
  /* |h2| <= 1.41*2^60 */
  /* |h6| <= 1.41*2^60 */

    carry2 = (hr[2] + (long) (1<<25)) >> 26; hr[3] += carry2; hr[2] -= carry2 << 26;
    carry6 = (hr[6] + (long) (1<<25)) >> 26; hr[7] += carry6; hr[6] -= carry6 << 26;
  /* |h2| <= 2^25; from now on fits into int32 unchanged */
  /* |h6| <= 2^25; from now on fits into int32 unchanged */
  /* |h3| <= 1.71*2^59 */
  /* |h7| <= 1.71*2^59 */

    carry3 = (hr[3] + (long) (1<<24)) >> 25; hr[4] += carry3; hr[3] -= carry3 << 25;
    carry7 = (hr[7] + (long) (1<<24)) >> 25; hr[8] += carry7; hr[7] -= carry7 << 25;
  /* |h3| <= 2^24; from now on fits into int32 unchanged */
  /* |h7| <= 2^24; from now on fits into int32 unchanged */
  /* |h4| <= 1.72*2^34 */
  /* |h8| <= 1.41*2^60 */

    carry4 = (hr[4] + (long) (1<<25)) >> 26; hr[5] += carry4; hr[4] -= carry4 << 26;
    carry8 = (hr[8] + (long) (1<<25)) >> 26; hr[9] += carry8; hr[8] -= carry8 << 26;
  /* |h4| <= 2^25; from now on fits into int32 unchanged */
  /* |h8| <= 2^25; from now on fits into int32 unchanged */
  /* |h5| <= 1.01*2^24 */
  /* |h9| <= 1.71*2^59 */

    carry9 = (hr[9] + (long) (1<<24)) >> 25; hr[0] += carry9 * 19; hr[9] -= carry9 << 25;
  /* |h9| <= 2^24; from now on fits into int32 unchanged */
  /* |h0| <= 1.1*2^39 */

    carry0 = (hr[0] + (long) (1<<25)) >> 26; hr[1] += carry0; hr[0] -= carry0 << 26;
  /* |h0| <= 2^25; from now on fits into int32 unchanged */
  /* |h1| <= 1.01*2^24 */

    h[0] = (int)hr[0];
    h[1] = (int)hr[1];
    h[2] = (int)hr[2];
    h[3] = (int)hr[3];
    h[4] = (int)hr[4];
    h[5] = (int)hr[5];
    h[6] = (int)hr[6];
    h[7] = (int)hr[7];
    h[8] = (int)hr[8];
    h[9] = (int)hr[9];
  }
}
